Here's what has gone missing as the franchise progressed:
- Branded after-market parts
- Exhaust upgrades showing up cosmetically
- Clear audible change in pitch, tone and character between street, sport and race engine upgrades (cams and exhausts)
- Diffusers improved the handling a lot, miss those
- No cap on controller steering (the trend started after FM3)
- Multiple home spaces
- Worthwhile drag racing
- Many cars that were previously upgradable to nearly 1000 HP or more now hover just around 750 HP after max upgrades
- In 5, when you would pan around to a 45 degree angle in cockpit view, you'd hear and feel the engine/exhaust more, particularly in rear-engine cars due to one of your ears pointing directly at the engine
- General lack of changes in engine audio character after upgrades
- Forza Vista engine start/rev sound has gotten sucky, whereas the same cars sound really good during races
These are only some of the things I remember off the top of my head. If I sit down to play previous FM games, I can point out more stuff, but what's the use, right?